The thruster system is used to adjust a position of a vessel, a marine structure, or the like, which floats on the water surface, and to control the vessel, the marine structure, or the like. The thruster system is mainly installed on a lower portion or in the interior of the vessel or the marine structure, and moves the vessel or the marine structure to a necessary position or maintains the current position of the vessel or the marine structure while being rotated in a lateral direction or in an arbitrary direction.
The thruster system may perform dynamic positioning that measures the current position and moves to a target position while compensating for disturbance such as tidal flows and waves, or may maintain the current position of the vessel or the marine structure in order to approach a harbor or the marine structure.
The thruster system may be classified into an omnidirectional thruster system and a tunnel type thruster system. The omnidirectional thruster system may control a position of the vessel or the marine structure through one or a plurality of thrust direction control operations. The tunnel type thruster system may implement lateral movement and rotation, thus having two types of degrees of freedom, and is mainly used to allow the vessel to approach a pier.
The thruster system is installed on a lower portion of a hull, and as a result, the thruster system protrudes from the lower portion of the hull. Therefore, the thruster system becomes a resistive body while the vessel sails, which causes deterioration in sailing efficiency of the vessel. In addition, since the installation of a thruster is mostly performed at the lower portion of the hull, work by a diver is necessarily required, and as a result, work for installing/dismantling the thruster is dangerous and complicated, and efficiency in installing/dismantling the thruster deteriorates. Furthermore, when the thruster system fails while the vessel sails, repairing the thruster system is complicated, and the thruster system protrudes from the lower portion of the vessel, which also makes it difficult to redock the vessel in order to repair the hull.
In order to solve the aforementioned problem, a retractable thruster system has been suggested. The retractable thruster system allows the thruster to protrude to the outside of the hull in a dynamic positioning mode (DP mode), and allows the thruster to retract into the hull while the vessel sails.
The retractable thruster system accommodates the thruster in a structure that is called a canister, and may move the canister up to a position for performing maintenance of the thruster.
The retractable thruster system moves the canister using a rack gear and a pinion gear, or moves the canister using a repetitive operation of a cylinder having a short stroke.
In a case in which the canister is moved by the rack gear and the pinion gear, a length of the rack gear needs to be greater than a stroke of the canister. Therefore, a length of the rack gear and a height of the canister may be increased. In a case in which a length of the rack gear is increased, evenness needs to be uniformly maintained, and as a result, there is a problem in that installation precision becomes higher.
In addition, in the case of the thruster system using the cylinder, a fixed position of the cylinder needs to be continuously changed in order to prevent an increase in length of the cylinder that lifts the canister, and as a result, there is a problem in that operations of installing and disassembling the cylinder need to be repeatedly performed.
In order to solve the aforementioned problems, a thruster system using a wire (Samsung Heavy Industries Co., Ltd.; Korean Patent Application No. 10-2011-0037188) has been suggested. In the case of the suggested thruster system, the upward movement of a canister is performed by tensile force that pulls the wire upward, and the downward movement of the canister is performed by a weight of the canister.
When the canister is moved downward from the water surface, buoyancy is applied to the canister, and as a result, a weight of the canister may be less than buoyancy. In this case, a reversed load occurs due to buoyancy, such that the canister connected to the wire may not be normally moved downward.